We need to focus on the other direction. How can we have chains of trust for content creation, such as for real video. Content can be faked, but not necessarily easily faked from the same sources that make use of cryptographic signing. The attacks can sign the own work, so you'd need ways to distinguish those cases, but device level keys, organizational keys, distribution keys all can provide provenance chains that can be used by downstream systems to _better_ detect fraud, though not eliminate it.